Hoping someone has found a way to make this work. I feel like we're almost there...but still not able to successfully test and use this connection.
We have a customer who is not using commercial M365, but GovCloud. Out of the box, the URLs point to "microsoft.com"---but we will use "microsoft.us". We have tried updating the URLs to reflect that, and working with the Portal admin team, they have created OAuth token endpoints that seemingly should be working. We are using the client secret method.
We put together some powershell to validate the connection and we are able to connect via Powershell using the Connect-AZ* cmdlets to validate connectivity is good. We just can't get the Beacon connector to connect successfully.
Flexera Support has told us GovCloud is not "officially supported"--but may work with some URL tweaks.